An induction charging apparatus, in particular a hand-held power tool induction charging apparatus, with an induction charging device for inductively charging an induction rechargeable battery device is discussed in DE 102013212611 A1. The inductive transmission of energy takes place via a primary oscillating circuit in the induction charging device and a secondary oscillating circuit in the induction rechargeable battery device. The oscillating circuits are inductively coupled to one another via at least one primary-side charging coil and one secondary-side charging coil, the resonant frequencies of the oscillating circuits ideally being approximately equal. The excitation of the primary oscillating circuit takes place via a rectangular-pulse signal that is formed by half-waves and generated in the induction charging device by an inverter. For this purpose, the inverter is appropriately controlled by a control or regulation unit, the frequency of the exciting rectangular-pulse signal typically being slightly above the resonant frequency of the oscillating circuits. This offers the major advantage of a so-called quasi-resonant operation with correspondingly low EMC interference levels and energy losses. It is also known that only those harmonics of the exciting signal in the proximity of the resonant frequency of the system contribute to a significant charging current. This is the fundamental mode of the rectangular-pulse signal.
A so-called IU or constant current constant voltage (CCCV) charging method for charging a rechargeable battery, in particular a lithium-ion rechargeable battery, is discussed in DE 102010003703 A1. In this method, the rechargeable batteries are charged in a first phase (I charging) at constant current while the charging voltage increases. The current is limited by a current controller of the charging device. After a selected end-of-charge voltage in the rechargeable battery is reached, in a second phase a switch is made from constant current control to voltage control (U charging), in which the rechargeable batteries are further charged at constant voltage and reduced charging current. This second phase is also referred to as the “current tail.”
In order to keep the exciting voltage in the current tail from further increasing, in the known induction charging devices the duty cycle of the exciting signal is reduced. However, the advantages of the quasi-resonant operation are thus lost.